Light emitting diode (LED) driver is an important component of solid state lighting devices which became the lighting technology of choice for energy efficient environmentally friendly lighting. Currently, the most common solution is to apply pulse width modulation (PWM) to generate constant forward current and to control brightness by adjusting duty cycle. Depending on the input voltage, the output current and power, isolation, and other requirements a variety of PWM topologies have been used for LED driver, including buck, buck-boost, flyback, and SEP IC (Single Ended Primary Inductor Converter) topologies.
While PWM principle has been used in constant-current sources for decades, use of the PWM principle for LED lighting applications presents a number of challenges. One of the most challenging applications is in retrofit lamps that are defined as lamps compatible with existing sockets and fixtures designed for incandescent, halogen, fluorescent, compact florescent, and metal halide lamps and meet illumination requirements including Color Rendering Index (CRI). First, the LED driver must fit into a form factor defined by an evacuated glass vessel and developed over 100 years ago commonly known as A19 bulb or fit onto a standard body of a reflector lamp such as GU10 or a PAR. Next challenge is thermal management. In a LED lamp, all energy which is not converted into visible light will be turned into heat dissipated in the driver and emitter. Driver efficiency becomes an important factor as it affects heat generation and overall efficiency of the lamp. Further, the reliability of an LED driver must match 50,000 h—the life expectancy of an LED emitter. An LED lamp is expected to operate at case temperatures exceeding 100° C. and to cycle between ambient and operating temperatures several times a day which is equivalent to more than 10,000 thermal cycles over 10 year life. Thus, Current Joint Electron Devices Engineering Council (JEDEC) standards of thermal cycling reliability in the range of 500-1000 cycles are clearly not sufficient for retrofit LED lights. In addition, as a switched mode power supply, an LED driver requires optimization to meet power factor and EMI (Electromagnetic Interference) requirements. Once form factor, thermal management, efficiency, and reliability problems are solved, the cost becomes yet another problem, as high-grade 125° C., or higher rated components, must be used and design complexity increases to meet all the requirements discussed above.
The current method of LED driver manufacturing uses conventional printed circuit boards (PCB) with standard packaged components. However, such conventional PCBs' cannot meet the efficiency, thermal management, reliability and cost requirements discussed above. Therefore, there is a need to provide an improved LED driver solution which solves the above-discussed problems.